DESCRIPTION: Exposure of cells to ionizing radiation can lead to long term consequences including cell killing, transformation and mutagenesis. Studies of early physico-chemical events that contribute to DNA damage are necessary to achieve a mechanistic understanding of the effects of ionizing radiation in cells. We propose that electron transfer represents a significant component of early events occurring in multiply damaged sites in DNA following exposure to ionizing radiation. In the investigator's initial work they have shown that radiation-induced electron migration along DNA is an important factor governing distribution of initial radiation damage. Using 5-BrU as a molecular probe to study electron interactions in model DNA systems, the investigators demonstrated that electron migration is both sequence and conformation dependent, that electrons were capable of migrating short distances along DNA and that electron transfer occurred preferentially in the 5' to 3' direction. In addition to the influence of electron transfer in mechanisms underlying radiation-induced damage occurring in multiply damaged sites, understanding mechanisms of charge transfer along DNA has clinical relevance for the rationale design of agents that affect cellular radiosensitivity. To further elucidate the mechanisms of electron transfer in nucleic acids we will: 1) determine the relative proportion of electrons capable of migrating along DNA that originate within the DNA, the primary layer of hydration, or the bulk water; 2) determine whether electrons are preferentially migrating through the overlapping _-electron orbitals created by stacked nucleobases in the DNA:water complex; 3) investigate whether electrons are capable of interstrand migration; 4) determine whether electrons are capable of transferring out of the migration pathway(s) along DNA into proteins; and 5) determine the sequence specificity for electron migration in DNA irradiated in vitro and in vivo. Overall, the investigator's work will shed light on the mechanisms by which electrons migrate along DNA and the physico-chemical and biochemical factors that influence migration. This work will contribute to a more detailed understanding of the mechanistic basis underlying deposition of radiation damage in multiply damaged sites in DNA and BrdU radiosensitization.